This invention relates to a dental measuring device, or bite gauge, for measuring the separation of reference positions relative to a patient""s upper and lower jaws.
To facilitate construction of comfortably fitting dentures or other fixed or movable dental prosthetics it is desirable to know the natural vertical separation at rest, or in a relaxed condition, of a patient""s upper and lower and lower jaws.
There are however, problems associated with the selection of appropriate reference points and with the accurate measurement of the separation of these points in so far as the selected points may lack precise definition and their vertical separation depends on the state of relaxation of the patient.
One known technique (xe2x80x98nose point to chin pointxe2x80x99) involves the use of conventional measuring tools, such as dividers or a micrometer gauge, applied between an upper point on the tip of the patient""s nose and a lower point on the patient""s chin. These are arbitrary points. It is usual to determine the spacing of the points in a rest position and also when the patient""s teeth are biting together. It is considered optimum to have a differential between the two readings of say 2-3 mm.
It has also been proposed to measure the distance between an ear and adjacent eye, specifically between the patient""s external auditory meatus and the adjacent lateral border of the ocular orbit, on the assumption that this bears a fixed relationship to a vertical separation of that patient""s upper and lower jaws. This assumption is however not necessarily correct in all cases and the measuring technique can be inconvenient or undesirable since it involves applying a measuring tool in close proximity to the patient""s eye.
Another known technique (xe2x80x98under nose to under chinxe2x80x99) uses a micrometer gauge having one of its measuring arms reversed so as to point in the opposite direction to the other arm. One arm, which is fixed at the end of a calibrated elongate member, is positioned under the patient""s nose (nasal spine) and the other arm, which is slidable along the member, is position beneath the chin (under mandible). The slidable arm is fixed in an adjusted position on the member with a screw, and the separation of the arms can be measured along the member. This technique, like the above nose point to chin point technique, is used to give readings at rest and biting positions.
The xe2x80x98nose point to chin pointxe2x80x99 and xe2x80x98under nose to under chinxe2x80x99 techniques are both commonly used. The former technique only provides a reading of the separation of the two arbitrarily selected points. The latter technique may not always provide reproducible readings in so far as the reading is dependent on the compression force applied to the patient""s tissues when the readings are taken, Accordingly it is usual for a decision to be taken as to which technique is preferred for each patient, dependent on factors such as the presence of any beard, angle of bone structure, and chin fat.
However, an instrument suitable for use with one technique may not be readily suitable for use with the other technique. Thus, a conventional micrometer gauge which is calibrated to give a reading of the separation of inner confronting surfaces of its arms when they are pointing in the same direction is suitable for use in the nose point to chin point technique but may not be suitable for use in the under nose to under chin technique since, with the reversed use of the gauge it is the separation of the outer surface of the under-nose arm and inner surface of the under-chin arm which is required. Also, with the reversed use of the gauge the usual scale and pointer will no longer be in juxtaposition. The desired measurement can not therefore be read off quickly and conveniently.
An object of the present invention is to provide a dental measuring device which is simple and convenient to use in both xe2x80x98nose point to chin pointxe2x80x99 and xe2x80x98under nose to under chinxe2x80x99 techniques, and with which accurate, reproducible measurements can be readily established for both such techniques.
According to the invention therefore there is provided a dental measuring device comprising a pair of measuring elements adapted for interconnection by a guide structure so as to be movable towards and away from each other along an axis, and a measurement indicating means operable to provide a readable indication of the separation of the measuring elements along the said axis, wherein the elements are adapted for interconnection in two modes, whereby in one mode they extend in different directions for positioning of contact surfaces thereof respectively under the nose and chin of a patient, and in a second mode they extend in a common direction for location relative to reference points on the nose and chin of a patient, and wherein the measurement indicating means is operable to provide said readable indication pertaining to the separation of said measuring elements in each said mode.
With this arrangement, the device can be used to give accurate, reproducible measurements for both nose point to chin point and under nose to under chin techniques.
The device is therefore a versatile, xe2x80x98all purposexe2x80x99 instrument, and the device can be used for purposes additional to the above techniques e.g. for measuring distances on models or dentures, measuring the distance between teeth, such as intercanine distance, measuring width of teeth etc.
In the said one mode, the measuring elements are preferably directed in opposite directions, particularly diametrically opposite directions. The invention is however not restricted to this and other dispositions may also be possible e.g. with the measuring elements transversely, particularly perpendicularly, to each other.
In the said second mode, the measuring elements preferably extend in the same direction particularly in the manner of a conventional micrometer.
Adaption of the device for selection of the modes is preferably effected by selective interfitting or positional adjustment of the measuring elements relative to each other e.g. by reversal of one element relative to the other.
The measurement indicating means is appropriately adaptable so as to provide a readable indication in each mode.
Such adaptation of the measurement indicating means may be effected by selective positional adjustment or selective substitution of parts of the measurement indicating means.
The measurement indicating means may have parts comprising at least one elongate calibrated scale and at least one pointer whereby the measurement indication is established by the location of the pointer along the scale. There may be two or more pointers and/or two or more scales so that in each mode there is a respective arrangement of a juxtaposed pointer and scale to ensure presentation of readily readable measurement indications corresponding to the respective mode.
Thus, for example, there may be pointers at different longitudinal positions relative to the scale, e.g. corresponding to the difference between measurement of the separation of the said contact surfaces in the said one mode and the measurement of the separation of tips, or inner confronting faces of the measuring elements in the said other mode.
The measuring elements are preferably rigid elongate arms which have free ends and which may be tapered towards such ends. In the case where the arms can be arranged in a mode in which they extend in the same direction, the free ends, in such mode, may be level with each other, and preferably the arms are of the same length. Preferably also the elements extend along respective axes which are parallel to each other.
Preferably the elements are movable relative to each other along a straight axis to which the elements extend perpendicularly.
The guide structure for guiding relative movement of the measuring elements preferably comprises an elongate member slidable through a sleeve, the measuring elements being fixed respectively relative to the member and the sleeve. Other guiding arrangements are however also possible.
Most preferably the guide structure is such as to ensure maintenance of relative angular dispositions of the said contact surfaces of the elements during adjustment movement. Preferably also, a releasable retention device is provided to hold the elements in adjusted positions. The retention device may comprise a frictional interfit, although a ratchet arrangement, or a locking screw or any other suitable device may also be used.
The measurement device may also include a hand grip, or handle, fixed relative to one of the measuring elements to facilitate holding of the device whilst permitting adjustment of the other of the elements. Suitable, the hand grip or handle may be an elongate structure which may be fixed to the aforesaid sleeve.
Where the measurement indicating means comprises a scale and pointer as aforesaid, the scale may be fixed relative to the said sleeve e.g. on the aforesaid handle or hand grip, and the pointer may be provided on the elongate member which is slidable within the sleeve.
Where the elongate member is reversible within the sleeve for adaptation between the different modes, there may be different pointers on opposite sides of the elongate member for adaptation of the measurement indicating means to correspond to the different modes.